U.S. Pat. No. 4,787,356 discloses a carburetor of this kind wherein the rpm of the engine, such as a two-stroke engine, is controlled when reaching a limit rpm by enriching the mixture in such a way that an overpressure acts on the control membrane with the overpressure being derived from an engine blower spiral or an engine muffler. The control membrane acts in opposition to the force of a spring by means of a centrally mounted pin on a carburetor regulating membrane. The carburetor regulating membrane opens a valve needle via a lever mechanism and thereby permits the flow of fuel into a pressure chamber. The force transmitted by the pin of the control membrane is directed via a bolt, which is mounted on the control membrane, to a free leg of a Z-shaped pivotally journalled transmitting lever and pivots the transmitting lever against the force of a spring. The other end of the transmitting lever is attached to a valve needle which blocks the throughflow of fuel. The valve needle is lifted from its valve seat by the pivoting of the Z-shaped transmitting lever and permits an increased enrichment of the air/fuel mixture via the fuel which now flows. The rpm drops with the enrichment of the mixture. A specific limit rpm cannot be exceeded.
Furthermore, the engine is cooled in the critical range (that is, high rpm and high temperature) additionally by the vaporization enthalpy of the fuel and is lubricated by the oil contained in the fuel.
As further described in U.S. Pat. No. 4,787,356, the arrangement is equipped with a solenoid actuator mounted on the dry side of the carburetor regulating membrane as an alternative to the control via the overpressure-dependent control membrane. The armature of the solenoid actuator acts via the control membrane on the lever mechanism described above and thereby opens the valve. The solenoid actuator is supplied with electrical voltage proportional to rpm. This causes a larger fuel throughflow and therefore an enrichment of the mixture. This, in turn, achieves a throttling of the engine and a specific limit rpm is not exceeded. It is a disadvantage in this arrangement that the solenoid actuator is mounted on the dry side of the regulating membrane. This causes more space to be needed for mounting the solenoid actuator and the carburetor housing must be correspondingly increased.
Both of the above-mentioned arrangements are in addition disadvantageous in that the long transmitting path defined by control member, carburetor membrane and transmitting lever requires a great many parts which must be mechanically or electromechanically moved. On the one hand, this causes a greater inertia of the system and, on the other hand, the inherent elasticity of the transmitting members as well as play and slack between two transmitting members cause additional delays which are in opposition to a desired precise control,
The configuration of these devices for limiting speed is most complex and very sensitive to disturbance.